Expendable wave guide pattern and method of manufacture



Sept. 4, 1956 COURTER 2,761,187

EXPENDABLE WAVE GUIDE PATTERN AND METHOD OF MANUFACTURE File d March 27,1952 IN VEN TOR. DONOM/V R COUR TE R A T TORNE Y Unite States EXPENDABLEWAVE GUIDE PATTERN AND METHOD OF MANUFACTURE This invention relates toimprovements in techniques and facilities for manufacturing wave guidesand particularly to the manufacture of wave guides including one or moreintegrally formed chokes.

A wave guide is a tubular member of. either rectangular or circularsection and of precise dimensions and, as the name implies, is used forguiding or directing ultra high frequency (UHF) energy or so-calledmicrowaves. A wave guide for use in combining systems is generallyprovided with a so-called choke at one or more of its open ends toreduce power leakage at the joints between connected guides. In additionto providing a flange to which a second flanged guide may be aifixed,such a choke includes a so-called energy ring or wave trap in the natureof an annular channel surrounding the central guide bore. The trap formsa short circuit which blocks wave propagation in the joint.

The tubular portion of wave guides are presently either fabricated,electro-formed or cast, the choke or chokes being formed or afiixedthereon subsequent thereto. Chokes are presently machined eitherindependently of the guide and thereafter afiixed to the guide or from ablank cast on an end of the guide. Reject rat-e on a fabricated guidenormally runs from 20 to 40%, and although the reject rate on a castguide with an integral choke blank is somewhat better, the cost of thisprocedure is almost prohibitive. I have now developed a method andapparatus for casting a wave guide as a unit including a choke in itsfinished form, the method involving adaptations of the principles oflost wax casting and the utilization of an expendable pattern ofparticular configuration and design.

In lost wax casting an expendable pattern is produced from a permanentmold, the pattern is sprued on an acceptable support and casting plasteris poured around the pattern. After the plaster has hardened it isusually heated to liquify or vaporize the expendable pattern material,whereby it is removed from the mold, leaving a plaster mold in which theend product is cast. The mold is, of course, destroyed in removing theend product and the procedure is repeated for each item. I have nowdeveloped an expendable pattern for a wave guide choke which is sodesigned as to form an integral part of an expendable wave guide patternwhich, upon use in the above described procedure, will result in a waveguide including an integrally formed and finished choke. The inventionpermits of close tolerances and etfectuates major economies inelimination of complex machinery operations.

In one aspect, therefore, the invention contemplates an expendablepattern for Wave guide chokes comprising a plate having obverse andinverse faces, a central port traversing the plate and comprisingstepped sections enlarging away from the obverse face, an annularintegrally formed lip projecting from the inverse face and defining anannular channel opening at the obverse face and deeper than the plate,an annular groove in the obverse atet face concentric with the lip, theplate forming a projecting flange outwardly of the groove.

In using the above described apparatus an expendable pattern for thetubular portion of the wave guide is extended into the port and bottomedtherein upon a shoulder formed between stepped sections, so that whenthe entire pattern is sprued and enclosed in plaster in the manner abovedescribed a plaster mold of a complete wave guide results.

In a preferred embodiment of the invention the central port in theexpandable pattern includes an integral tubular extension projectingfrom the inverse face of the guide and defining in part the steppedsections of the port. The walls of the tubular extension are taperedoutwardly from the central axis of the port throughout that portion ofthe extension which defines the larger of the port sections. The taperis such that the inside dimensions increase toward the outer end of theextension while the outside dimensions remain constant. This preferredembodiment has the advantage of permitting the casting of the expendabletube pattern in association with the expendable choke pattern, therebyeliminating the need of manual assembly between the tube and chokepatterns.

In addition to the expendable pattern itself the invention contemplatesthe method of casting a wave guide comprising forming an expendablechoke pattern having a port enlarged in part to a size larger than theinternal cross section of the desired guide, forming a tubular patternof expendable material corresponding to the dimensions of the desiredguide with the latter extending into and bottomed in the enlarged partof the port, forming a plaster mold around the expendable pattern,eliminating the expendable pattern from the plaster mold and casting thedesired wave guide in the resultant plaster mold.

Again, preferred practice constitutes casting the tubular expendablepattern in a cavity mold and in conjunction with the choke pattern sothat no manual pattern assembly is required.

The invention will be more clearly understood by reference to thefollowing detailed description taken in conjunction with theaccompanying drawing in which:

Fig. 1 is a front elevation of an expendable choke pattern in accordancewith the invention;

Fig. 2 is a rear elevation of a preferred form of an expendable patternin accordance with the invention;

Fig. 3 is a sectional elevation through a pattern mold showing thepattern of Fig. 2 in sectional elevation and the means of using thechoke pattern in forming an expendable guide pattern;

Fig. 4 is a revolved elevation of in the mold of Fig. 3;

Fig. 5 is a rear elevation of another form of pattern in accordance withthe invention;

Fig. 6 is a sectional elevation taken on the line 6-6 of Fig. 5; and

Fig. 7 is a sectional elevation through another embodiment in accordancewith the invention.

Referring to Figs. 1, 2 and 3 of the drawing, the expendable patternthere shown comprises a plate 10 having an obverse face 10A and aninverse face 103 shown in Figs. 1 and 2 respectively. The plate has acentral port 12 defining the cross sectional opening of the desired waveguide, the port forming stepped sections 12A, 12B and including atubular extension 14 (see Fig. 3) projecting from the inverse face ofthe plate. The sides of the tubular extension taper outwardly away froman extension of the center line of the port 12 for reasons hereinaftermade apparent. The stepped sections 12A, 12B of the port form a shoulder12C which serves a function hereinafter made apparent.

An annular lip 16 projects from the inverse side 10B of the platedefining an annular groove 16A opening at the pattern developed theobverse face A of the plate, the groove 16A forming the short circuitingwave trap heretofore mentioned. An annular groove 18 is formed in theplate exteriorly and concentrically with the grooveil6A, thegroove 18forming a housing for an O ring or other sealing gasket (not shown).

'In. using the pattern 10 to produce an expendable wave guide, pattern,a pattern mold 20 is provided with a cavity 21 defined by membersZtlA,20B. The member2tlB has a bore 22 defining the exterior dimensions ofthe desired wave guide and opening on the central axis of the cavity 21.The mold section 20A has a bore 24 to receive a core 26 mounted throughthe bore 24 and extending into the bore 22. The core 26 defines theinterior dimensions of the wave guide forming an annulus within the bore22 corresponding with the wall thickness of the wave guide.

.Pattern 10 is mounted in the cavity 241! shown, the integral tubularprojection 14v extending into the bore 22 and engaging against the wallsthereof. The core 26 passes through port 12 of the pattern, section 12Aof which is dimensioned to correspond to the inside of the wave guideand hence the core dimensions. As illustrated, the core 26 is spacedfrom the walls of bore 22 in mold section ZtlB thereby defining anannular passageway in the mold sections. When wax or other expendablepattern material is poured into the mold it flows into this passagewayas illustrated in Fig. 3 to form a tubular pattern 28. The injected waxis excluded from the cavity 20 by the seal formed between the tubularextension 14 and the walls of the mold bore 22 and forms a comparativelyrugged connection with the expendable choke pattern 10 through a unionbottomed on the annular shoulder 12C and extending along the innersurface of the larger section 12B of the port as defined in part by thetapered walls of the integral tubular extension 14.

The wax injected in the annular passageway formed between the core 26and wall of bore 22 in mold section 20B thus forms an annular tube whichextends into the stepped sections in the pattern member 11 and forms anintegral part with the member 10 of the wave guide pattern. Thecomposite pattern may then be withdrawn fromthe mold and employed inaccordance with conventional lost wax casting techniques to form a waveguide. This is accomplished by spruing this expendable pattern on asupport and coating it with a refractory material such as castingplaster. The casting plaster is allowed to'set around the pattern whichis then disposed of byburning it or melting it out of the plaster mold.Molten metal may then be poured into the refractory mold to form thewave guide.

Fig. 4 is an elevation view of the revolved pattern as developed in themold of Fig. 3.

A somewhat simpler form of the invention is shown in rear elevation inFig. 5 and sectional elevation in Fig. 6. Pattern 30 shown in thesefigures is similar to pattern 12 heretofore described, differingtherefrom. only in the absence of the integral tubular extension 14. Inthe pattern 30 a port 32 is undercut from the inverse side 30B to formstepped sections 32A, 32B defining a .circumscribing shoulder 32C. Anintegrally formed lip 34 corresponding to the-lip 16 of the abovedescribed embodiment projects from the inverse side 30B of the plate anddefines a channel opening in the obverse face of the plate. In thisparticular embodiment the lip 34 is undercut or broached at 34A todefine a continuation of the larger section 32B of .the port' 32, sothat a tubular wax pattern of exterior dimensions conforming to thissection of the port can be inserted and bottomed on the shoulder 32C.The broached portion of the lip34 helps support such a tube, which maybe additionally supported'by moistening the edges of the port section323 with suitable solvent .to temporarily soften at that point theexpendable material from which the choke patternis made.

" The" embodiment shown in sectionalel'evationin' Fig. 7

is a pattern for a wide band choke which is characterized by a somewhatshallower but thicker (radial dimension) wave trap. This patterncomprises a plate 40 having obverse and inverse faces 40A, 4013respectively, a central port 42 including an integral tubular extension44 defining stepped port sections 42A, 42B. As in the embodiment of Fig.3, the walls of the tubular extension forming the larger of the two portsections are tapered and for the same purpose. In this respect thispattern differs from that of Fig. 3 in that the circumscribing step orshoulder 42C formed by the stepped sections is displaced on the axis ofthe port so that a tubular wax pattern associated therewith does notextend as far into the port. The configuration of the port definingtubular extension 44 of this figure may be employed as an alternativearrangement of the pattern of Fig. 3.

The plate 45) is provided with an annular lip 46 projecting from theinverse face and defining a channel 47 opening at the obverse face, thelip and channel differing from the corresponding elements of theforegoing embodiments in being shallower and of larger radialdimensions. A concentric annular channel 48 in the obverse face 40A ofthe plate is adapted to receive a sealing ring as above described.

The choke pattern of the invention may be made from any expendableplastic, styrene being the presently preferred form of plastic.Dimensional stability and a certain amount of rigidity are of courseessential. The pattern of the invention can be turned out in largequantities and sold for use anywhere in the country; it is extremelyeconomical and experience shows that there are practically no rejects ofthe finished molds.

I claim:

1. An expendable pattern for wave guides comprising a plate havingobverse and inverse faces, a central port traversing the plate andcomprising stepped sections enlarging away from the obverse face, anannular integrally formed lip projecting from the inverse face radiallyof the center port and defining an annular channel opening at theobverse face and deeper than the plate, an annular groove in the obverseface concentric with and radially of the channel, the plate forming aprojecting flange outwardly of the groove.

2. An expendable pattern for wave guides comprising a plate havingobverse and inverse faces, a central port traversing the plate andcomprising two stepped sections enlarging away from the obverse face andforming a circumscribing rearwardly facing shoulder at their juncture,an annular integrally formed lip projecting from the inverse faceradially of the center port and defining an annular channel opening atthe obverse face and deeper than the plate, an annular groove in theobverse face concentric with and radially of the channel, the plateforming a projecting flange outwardly of .the groove.

3. An expendable pattern for wave guides comprising a plate havingobverse and inverse faces, an annular integrally formed lip projectingfrom the inverse face and defining an annularchannel opening at theobverse face and deeper than the plate, a central port the central axisof which'coincides with the axis of the annular lip and comprising twostepped sections, the smaller section opening at the obverse face, anannular groove in the obverse face outwardly of and concentric with thelip, the plate forming a projecting flange outwardly of the groove.

4. An expendable pattern for wave guides comprising a plate havingobverse and inverse faces, a central port extending through the plateand comprising two stepped sections, an integral tubularextensionprojecting from the inverse face of the plate and defining the port, anannular integrally formed lip projecting from the inverse face radiallyof the center port and defining an annular channel opening at theobverse face and deeper than the plate, an annular groove in theobverseface concentric with and radially of the channel, the plate forming aprojecting flange outwardly of the groove.

5. An expendable pattern for wave guides comprising a plate havingobverse and inverse faces and a centrally disposed integral tubularextension projecting from the inverse face, a central port in the platedefined by a hole in the plate and said tubular extension, the portconsisting of two stepped sections, the smaller of which opens at theobverse face, an annular integrally formed lip projecting from theinverse face radially of the center port and defining an annular channelopening at the obverse face and deeper than the plate, an annular groovein the obverse face concentric with and radially of the channel, theplate forming a projecting flange outwardly of the groove.

6. An expendable pattern according to claim wherein the portion of thewalls of the tubular extension defining the larger of the port sectionstaper outwardly in inside dimensions so that the wall thickness of thetubular extension at its outer end is less than that adjacent the innerend of the larger port section.

7. A method of forming an expendable wave guide pattern for casting waveguides which comprises forming an expendable choke pattern including atubular extension defining a central port having stepped sections,mounting the pattern in a guide mold with the outer edge of the tubularextension sealing against the mold and with a mold core passingconcentrically through the central port and being spaced therefrom toform an annular passageway, injecting a normally solid expendablepattern material in fluid form into this passageway to form a continuoustube extending into the stepped sections of the choke pattern andbecoming an integral part with the choke pattern of a composite waveguide pattern.

8. A method of forming an expendable wave guide pattern which comprisespreforming an expendable choke pattern including a plate having acentral port in two stepped sections, mounting the choke pattern in amold with a mold core passing concentrically through the port andfitting snugly in the small port section and forming a concentricpassageway extending from the choke pattern, and injecting a normallysolid expendable pattern material in fluid form into this annularpassageway to form a tubular expendable pattern around the core andextending into and sealed in the larger port section whereby the tubularpattern and the choke pattern form an integral composite wave guidepattern.

9. A method of forming an expendable wave guide pattern which comprisespreforming an expendable choke pattern including a plate having acentral port and an integral tubular extension defining a continuationof the central port, the port constituting two stepped sections with theportion of the walls of the tubular extension defining the larger of thestepped sections flaring outwardly in inside dimensions, mounting thechoke pattern in a mold with the outer edge of the tubular extensionsealing against the mold and with a mold core passing concentricallythrough the port and fitting snugly in the smaller of the port sectionsand passing concentrically through a bore in the mold and being spacedfrom the walls of the bore to form an annular passageway therein,injecting a normally solid expendable pattern material in fluid stateinto the mold annular passageway to form a tubular pattern around thecore extending into the larger port section of the choke pattern andsealing against the flared wall portion of the tubular extension tobecome an integral part with the choke pattern of a composite wave guidepattern.

10. A pattern for wave guides comprising a plate having obverse andinverse faces, a central port traversing the plate and comprising twostepped sections enlarging away from the obverse face and forming acircumscribing rearwardly facing shoulder at their juncture, an annularintegrally formed lip projecting from the inverse face radially of thecenter port and defining an annular channel opening at the obverse faceand deeper than the plate, an annular groove in the obverse faceconcentric with and radially of the channel, the plate forming aprojecting flange outwardly of the groove.

11. A pattern for wave guides comprising a plate having obverse andinverse faces, a central port extending through the plate and comprisingtwo stepped sections, an integral tubular extension projecting from theinverse face of the plate and defining the port, an annular integrallyformed lip projecting from the inverse face radially of the center portand defining an annular channel opening at the obverse face and deeperthan the plate, an annular groove in the obverse face concentric withand radially of the channel, the plate forming a projecting flangeoutwardly of the groove.

12. A pattern for wave guides comprising a plate having obverse andinverse faces and a centrally disposed integral tubular extensionprojecting from the inverse face, a central port in the plate defined bya hole in the plate and said tubular extension, the port consisting oftwo stepped sections, the smaller of which opens at the obverse face, anannular integrally formed lip projecting from the inverse face radiallyof the center port and defining an annular channel opening at theobverse face and deeper than the plate, an annular groove in the obverseface concentric with and radially of the channel, the plate forming aprojecting flange outwardly of the groove.

13. An expendable pattern for wave guides comprising a plate havingobverse and inverse faces, a rectangular port opening through the centerof the plate and comprising two stepped sections, the larger sectionopening at the inverse face of the plate, an annular integrally formedlip projecting from the inverse face radially of the port and definingan annular channel opening at the obverse face and deeper than theplate, the lip having an inside diameter just less than the dimension ofthe major axis of the rectangular port and being undercut adjacentopposite ends of the port to form extensions of the end surfaces of thelarger port section.

14. A method of forming an expendable wave guide pattern for castingwave guides which comprises forming an expendable choke pattern defininga central port having stepped sections, mounting the pattern in a guidemold with a mold core passing concentrically through the central portand being sealed against the smaller of the stepped sections and spacedfrom the larger section and from the mold to form an annular passageway,injecting a normally solid expendable pattern material in fluid forminto this passageway to form a continuous tube extending into thestepped sections of the choke pattern and becoming an integral part withthe choke pattern of a composite wave guide pattern, removing thecomposite expendable pattern from the mold, coating the exterior of thepattern with a refractory material, allowing the refractory material toset, removing the expendable pattern from the set refractory materialand casting the wave guide in the resultant mold whereby the guide tubeand choke are integrally formed.

References Cited in the file of this patent UNITED STATES PATENTS1,675,732 Schweitzer July 3, 1928 2,456,424 Neiman Dec. 14, 19482,462,370 Drake Feb. 22, 1949 2,466,272 Porter et a1. Apr. 5, 19492,495,402 Bentsen Ian. 24, 1950 2,508,546 Skinner May 23, 1950 2,635,294Rolaston Apr. 21, 1953 OTHER REFERENCES Palmer: Foundry Practice, 3rdad, page 385 relied on; by John Wiley & Sons.

